India's Congress party rallies hundreds of thousands in Delhi

The leaders of India's ruling Congress party addressed a rare gathering of hundreds of thousands of supporters on Sunday, attempting to reclaim lost political ground after being battered by a series of corruption scandals.

The rally comes as a two key Indian states head to the polls and as the party begins preparations for national elections to be held in 2014.

Sonia Gandhi, the Italian-born leader of the Congress party, defended a series of politically unpopular economic reform measures launched by the government over the last few months. These include opening India's retail sector to foreign investment and cutting fuel subsidies.

In her fiery speech, Gandhi also addressed the corruption allegations her party and its allies have faced over the last two years.

"I admit, corruption is a cancer, it is a disease," she said. "We will continue to fight this disease."

Corruption scandals

Several government ministers are facing corruption charges stemming from scandals over the hosting of the 2010 Commonwealth Games, the sale of cellphone spectrum, and allocation of coal fields that auditors said lost the country of billions of dollars.

More recently, anti-corruption crusader Arvind Kejriwal has alleged that Gandhi's businessman son-in-law Robert Vadra made millions of rupees off of shady real estate deals and a senior minister embezzled millions of rupees meant for a charity that helps the disabled. None of Kejriwal's allegations have led to charges or been independently verified, but they have added to the government's graft woes.

The opposition Bharatiya Janata Party has used the corruption scandals to score political points but on Sunday Gandhi hit back.

"Those who dig a pit for others to fall should know that a well is waiting for them to fall into," she said, without naming the BJP directly.

Singh said India's stuttering economic growth could not be boosted without reforms and those opposing them were "misleading the people."

Rahul, a scion of the politically powerful Nehru-Gandhi family, is the son and grandson of two prime ministers. He is presumed to be a prime minister-in-waiting, but so far has held no government positions. His public appearances are rare and carefully chosen.

The political gathering came as the northern state of Himachal Pradesh began voting Sunday. Campaigning is also in full swing in Gujarat in western India where elections will take place in December.